• Board contributors include instructors with "800" GMAT scores.
  • 95% of posts have replies within 24 hours.
  • Join for discounts with 800score, VeritasPrep and ManhattanGMAT


FAQ  - Register  - Search - Login 

All times are UTC - 7 hours




Post new topic Reply to topic  [ 2 posts ] 
Author Message
 Post subject: GMAT Number Theory
PostPosted: Sat May 04, 2013 5:15 am 
Offline
User avatar

Joined: Tue Apr 13, 2010 8:48 am
Posts: 483
The sum of the digits of a three-digit number is 11. What is the product of the three digits?
(1) The number is divisible by 5.
(2) The hundreds digit is twice the tens digit.

A. Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.
B. Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.
C. Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.
D. Either statement BY ITSELF is sufficient to answer the question.
E. Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, meaning that further information would be needed to answer the question.

(C) Statement (1) alone is not sufficient because it tells us only that the number has a units digit of 0 or 5. If the number has a units digit of 0, the product of the digits will be 0 (since 0 times any number is 0), and if the number has a units digit of 5, the product of the digits might not be zero (depending on whether one of the other digits is 0).

For instance, the number 515 has digits that add to 11, yet the product of the digits is 25. Therefore, Statement (1) is insufficient.

Statement (2) is not sufficient by itself either. By choosing the tens digit starting from 1, we conclude the following. The number can be 218 or 425 or 632. The product of the digits is different in each case.

Combined, the two statements are sufficient. The only possibility is that the number is 425, and so the product of the digits is 40.

Since the statements are both insufficient individually but sufficient when combined, the correct answer is choice (C).
----------
This doesn't explain why the one's digit cannot be 0 when Statement 1 and 2 are combined.


Top
 Profile  
 
 Post subject: Re: GMAT Number Theory
PostPosted: Sat May 04, 2013 5:16 am 
Offline
User avatar

Joined: Fri Apr 09, 2010 2:11 pm
Posts: 459
Quote:
This doesn't explain why the one's digit cannot be 0 when Statement 1 and 2 are combined.
Statement (2) implies that there are only 3 options: 218, 425, and 632. None of them has 0 as a unit digit.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 2 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Template made by DEVPPL -
phpBB SEO
 
GMAT(TM) and GMAT CAT (TM) are registered trademarks of the Graduate Management Admission Council(TM). The Graduate Management Admission Council(TM) does not endorse, nor is affiliated in any way with the owner or any content of this site.